if the cat rattles it is broke up inside.  you are describing a dead cat
converter.
jimt

> Hi guys,
> driving from Pittsburgh to New Jersey, I ran into the following: first,
sudden loss of power, especially up hills, etc---pretty independent of
which gear your in.  Later, power returns, but engine is very
noisy---like a car without a muffler (although perhaps not quite that
noisy).  Other than that, the engine seems to run fine now, and the
noise, it seems, can only be heard from the outside---that is, with the
windows rolled up, driving on the highway, you don't notice it.  Roll
down the windows, or get out the car, and its VERY loud.
>
> My thought was: some ceramic in my catalytic converter broke up, at
first clogging the exhaust, but then breaking free and letting more
exaust through---thus returning the loss of power, but muffling the
engine noise less.  Does this sound right to people?  If not, what
should I be looking for?  And if so, I can just drive it like this until
I have to pass an emmissions test, right?  And how can I try to find a
cheap cat?
>
> Thanks very much for any help.  Oh---and the van's an '84 manual.
>
> Another thing I noticed---there is still "exhaust" coming out of the
tailpipe, but you wouldn't know it if you didn't stick your hand right
behind the tailpipe---it's not black at all.
>
> Thanks again,
> Wes
>